Rotaviruses, members of the family Reoviridae, are the most important cause of severe acute diarrhea in infants and young children and on an annual basis are responsible for nearly one million deaths worldwide. Their medical significance has stimulated extensive and successful efforts towards the development of rotavirus vaccines by the Laboratory of Infectious Diseases (LID) at the NIH. Specifically, a rotavirus tetravalent vaccine developed by the LID has been shown in large scale phase III trials to have an efficacy of protection against severe and life-threatening dehydrating diarrhea of 80 to 100%. The tetravalent vaccine has been approved for use in humans by the FDA and is marketed by Wyeth-Lederle. The limitations of the existing vaccine are that it is relatively expensive, less effective in preventing mild and moderate diarrhea due to rotavirus infection, and is designed to provide protection against only the four major circulating serotypes (G1-4) of rotavirus.The initial phase of this project focuses on the development of a reverse genetics system that can be used to alter the genetic information of the rotavirus genome. Subsequently, this system will be used as a tool in identifying loci within the genome that define the growth characteristics, antigenic properties, and virulence of rotaviruses. In the final phase of the project, the reverse genetics system will be applied to improving the growth characteristics of the vaccine viruses in cell culture, to increasing the immunogenicity of the vaccine, and to altering the antigenicity of the vaccine to include non-G1-4 serotypes. The reverse genetics system will also be used to create a new generation of potentially more effective vaccines by the introduction of attenuating mutations into the genome of virulent isolates of human rotaviruses. - Rotavirus, Infantile diarrhea, Vaccine development, Reverse genetics, Genetic engineering, Antigenicity, Virulence, Attenuation